This invention relates to percussion tools of the type in which a reciprocating hammer piston delivers repeated blows to a working implement introduced into the tool housing through a front opening therein. An example of tools of this type is a chipping hammer.
Usually, this type of tool is intended to be manually supported which means that the tool including the chisel connected thereto is applied onto a work piece by a trained operator. In previous tools the chisel is freely displaceable relative to the housing between a rear blow receiving position and a forward idle or rest position, and the operator has to take into account this difference in chisel tip position when moving the tool from one working position to another. When, for instance, using this type of tool removing a burr from iron castings the chisel is thrown over to its forward position each time the burr gives away, and when moving the tool into a new working position, i.e. applying the chisel tip against the burr still to be removed, the operator first has to retract the entire tool to ensure that the chisel tip is well behind the burr before moving the tool sidewise and reapply it on the burr. This is easily and automatically compensated for by the operator, because in hand held tools the axial displacement of the chisel relative to the tool housing is relatively small compared to the inevitable axial displacement of the entire tool when a breakthrough occurs.
When, however, mounting the chipping hammer on a mechanical support it is desirable to avoid any longitudinal displacement of the chisel relative to the tool housing to, thereby, facilitate the movement pattern of the tool relative to the work piece. This is obtained by employing a return spring by which the working implement is always returned to its blow receiving or rest position in the housing after each stroke.
A problem concerned with this type of spring biassed working implement is that the spring is exposed to a very severe strain resulting from the repeated impacts delivered by the hammer piston. This strain is caused by the shock waves which arise each time the working implement is hit by the hammer position, and the fatigue strength of the spring is not able to withstand this kind of treatment for a longer period of time.
The main object of the invention is to create an energy absorbing means which effectively reduces the shock wave stresses in the bias spring.
A preferred embodiment of the invention is hereinafter described in detail with reference to the accompanying drawing.